We evaluated glomerular lesions in kidneys from patients who underwent nephrectomy for renal cancer. In areas non-invaded by the tumor there was, in one-half of the cases examined, marked mesangial proliferation and occasional synechiae. This suggested that the glomerular lesions we found could be mediated by growth factors released from the tumor. In a separate group of patients we examined the effect of interleukin II on the kidneys of 19 patients who died in the Clinical Center. The occurence of lesions was correlated with the creatinine and BUN level.